Age-related dynamics of m.189A>G and m.408T>A variants in skeletal muscle of an osteoarthritic Cohort: Connections to BMI and muscle strength

The origin and expansion of mitochondrial somatic variants, influenced by tissue-specific mutagenesis and selection, are not well understood despite their relevance to aging and age-related diseases. Postmitotic tissues, such as skeletal muscles, are particularly underexplored, even though mtDNA variant evolution in these tissues can differ significantly from that in proliferative tissues. To address this, we analyzed mitochondrial heteroplasmy in skeletal muscle samples from an osteoarthritic cohort (N = 105). We observed that the age-related dynamics of two famous variants m.189A > G and m.408T > A in our cohort is indistinguishable from their dynamics in random control cohort, suggesting that they are not a cause of muscular problems, but rather mark the age-related processes in muscles. We also observed that when adjusted by age and gender, carriers of these variants tend to have higher BMI, body weight, and muscle strength than non-carriers. Putting together all the lines of evidence, we propose that these variants are able to rapidly expand through selfish dynamics, which is especially pronounced in hypertrophic muscle fibers of individuals with higher body weight. Further investigation is necessary to clarify this hypothesis.